Abstract
The distribution and specificity of extracellular nucleases produced by marine fungi belonging to eleven genera, namely: Alternaria, Aspergillus, Aureobasidium, Chaetomium, Fusarium, Gliomastix, Humicola, Penicillium, Scopulariopsis, Wardomyces, Periconia, have implied its important function in the organic phosphorus and nitrogen circle in the Ocean. The fungal nucleases of 64 isolates tested were more or less specific for single-stranded DNA with a high preferential specificity towards poly-U substrate with forming of 5’-phosphate mononucleotides. A couple of the nucleases were capable of RNA digesting. The highest level of extracellular nucleolytic ability was observed in Penicillium spp. isolates. The tight correlation found between extracellular nuclease activity and the rate of thymidine uptake by actively growing and sporulating marine fungus Penicillium melinii suggests that this nuclease is required for fulfilling the nucleotide pool of precursors of DNA biosynthesis during transformation of hyphae into the aerial mycelium and conidia in stressful environmental conditions.
Highlights
The main portion of the organic carbon, phosphorus and nitrogen is a direct result of enzymatic processing of dissolved macromolecules of DNA, RNA and proteins in aquatic environments due to their wide occurrence [1,2]
The tight correlation found between extracellular nuclease activity and the rate of thymidine uptake by actively growing and sporulating marine fungus Penicillium melinii suggests that this nuclease is required for fulfilling the nucleotide pool of precursors of DNA biosynthesis during transformation of hyphae into the aerial mycelium and conidia in stressful environmental conditions
The isolates of P. melinii and P. patulum isolated from colonial ascidium near Shikotan Island at the depth of 123 m and P. patulum isolated from Peter the Greate Bay bottom sediments, Sea of Japan, at the depth of 46 m showed a high level of extracellular nuclease activity (Table 1)
Summary
The main portion of the organic carbon, phosphorus and nitrogen is a direct result of enzymatic processing of dissolved macromolecules of DNA, RNA and proteins in aquatic environments due to their wide occurrence [1,2]. The contribution of marine mycobiota as a source and consumer of the dissolved organic matter such as nucleic acids has not been yet shown. It is known that a large group of fungi and filamentous bacteria generate and disseminate spores for implement of survival program in stressful environmental conditions. These events call forth increase of nuclease activity dramatically that coincides with lysis of the substrate hyphae and formation of aerial mycelium [6]. It has analogy to the late steps of apoptosis of other eukaryotic cells [7] These programs may be activated by environmental stresses or by natural processes of senescence [8,9]. Plant cells undergoing programmed cell death during tissue differentiation at the end of mitosis or under the influence of pathogens exhibit DNA degradation [10]
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